In the beverage service industry syrups and concentrates utilized for the preparation of soft drinks are normally provided in bulk containers for blending with the soft drink liquid base on a demand basis. The syrups are viscous and, in their undiluted state, somewhat reactive, and thus can interfere with the proper operation of conventional pump mechanisms utilizing a reciprocating piston which slides back and forth in a cylinder. In addition, conventional electrically operated pumps, when overloaded or stalled, can cause failure of the drive motor windings, thus requiring often extensive and expensive repairs as well as creating the possible risk of fire or damage to associated components as a result of excessive heating of motor windings in the stalled state. Pumps using electric motor drives further are also relatively bulky.
Pneumatically-operated pumps, in which one or more diaphragm-type pistons are utilized, are known in the art and are typically of a more compact size than electric pumps having a similar output capacity. In addition, such pneumatically-operated pumps are in practice driven by the same source of compressed gas, namely carbon dioxide, which is utilized to carbonate the liquid base. Such pumps have the further inherent advantage that an electrical supply is not required for their operation.
Conventional pumps of the pneumatic variety are exemplified by the teachings of U.S. Pat. Nos. 4,123,204 to Scholle and 4,540,349 to Du. In the Scholle pump, the driving compressed gas is directed to opposed piston chambers through a complex series of passageways and valves wherein the valve actuating stems contact stop members within the pump apparatus. The Du pump relies upon the longitudinal shift of a valve element by the alternate interaction between opposed internal pipe ends with the respective pistons as they oscillate.
Because of the complexity of the demands placed upon the valving apparatus which alternates the pressurization of the piston chambers, and the form and nature of the seals required between the moving parts and their fixed housings, pneumatic pumps are subject to leakage and often unexpected failure. As the valving is located deep inside the pump, the pump must be removed from the apparatus with which it is used and disassembled for repair or replacement purposes. Further, the life of the pump is a function of its operating time and thus the number of reciprocations which the pump has performed. It has heretofore been difficult to determine with any precision when the useful life of the pump is expiring, as conventional pumps have provided no means by which actual operation can be monitored.
It is accordingly a purpose of the present invention to provide a pump mechanism which may be driven by a compressed gas, rather than by an electric motor.
Another purpose of the present invention is to provide a pump which may operate effectively with viscous and/or reactive materials to be pumped.
Still a further purpose of the present invention is to provide a pneumatic pump of simple design and efficient manufacture.
Yet another purpose of the present invention is to provide a pneumatic pump in which the gas transfer valve system is of simple and rugged design, and which may be accessed and replaced without the necessity of disassembly of the pump.
A further purpose of the present invention is to provide a pump of the character described, wherein a counter-mechanism is incorporated into the pump to provide a direct reading of the number of pump reciprocations.